Question

A bag contains 3 red marbles and 4 blue marbles. A marble is taken at random from the bag and replaced. Another marble is taken from the bag.

Work out the probability that the two marbles taken from the bag are the same colour.

Give your answer as a fraction.

Answer 1

25/49

Explanation:

probability of red and red is (3/7)(3/7) = 9/49

Probability of blue and blue is (4/7)(4/7) = 16/49

Probability of same color = prob. of red and red or prob. of blue and blue

= 9/49 + 16/49

= 25/49